Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Assets
Land	$ 1,012,684	$ 1,003,422
Buildings and improvements	5,979,985	5,890,498
Real estate assets, at cost, total	6,992,669	6,893,920
Accumulated depreciation	(1,798,955)	(1,738,862)
Net operating real estate assets	5,193,714	5,155,058
Properties under development, including land	519,454	527,596
Investments in joint ventures	36,526	36,429
Properties held for sale	0	27,143
Total real estate assets	5,749,694	5,746,226
Accounts receivable – affiliates	25,652	25,977
Other assets, net	122,326	124,888
Cash and cash equivalents	174,353	153,918
Restricted cash	5,034	5,898
Total assets	6,077,059	6,056,907
Liabilities
Unsecured notes payable	1,838,203	1,837,911
Secured notes payable	904,914	905,628
Accounts payable and accrued expenses	134,438	157,232
Accrued real estate taxes	23,269	39,149
Distributions payable	64,261	60,386
Other liabilities	102,163	100,058
Total liabilities	3,067,248	3,100,364
Commitments and contingencies (Note 10)
Non-qualified deferred compensation share awards	69,902	68,134
Equity
Common shares of beneficial interest; $0.01 par value per share; 175,000 shares authorized; 100,646 and 100,620 issued; 97,586 and 97,604 outstanding at March 31, 2015 and December 31, 2014, respectively	976	976
Additional paid-in capital	3,656,105	3,667,448
Distributions in excess of net income attributable to common shareholders	(403,518)	(453,777)
Treasury shares, at cost (10,741 and 10,975 common shares at March 31, 2015 and December 31, 2014, respectively)	(388,181)	(396,626)
Accumulated other comprehensive loss	(2,382)	(2,419)
Total common equity	2,863,000	2,815,602
Non-controlling interests	76,909	72,807
Total equity	2,939,909	2,888,409
Total liabilities and equity	$ 6,077,059	$ 6,056,907